path: root/common/placer1.cc

/*
 *  nextpnr -- Next Generation Place and Route
 *
 *  Copyright (C) 2018  Claire Xenia Wolf <claire@yosyshq.com>
 *  Copyright (C) 2018  gatecat <gatecat@ds0.me>
 *
 *  Simulated annealing implementation based on arachne-pnr
 *  Copyright (C) 2015-2018 Cotton Seed
 *
 *  Permission to use, copy, modify, and/or distribute this software for any
 *  purpose with or without fee is hereby granted, provided that the above
 *  copyright notice and this permission notice appear in all copies.
 *
 *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "placer1.h"
#include <algorithm>
#include <boost/lexical_cast.hpp>
#include <boost/range/adaptor/reversed.hpp>
#include <chrono>
#include <cmath>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <ostream>
#include <queue>
#include <set>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <vector>
#include "fast_bels.h"
#include "log.h"
#include "place_common.h"
#include "scope_lock.h"
#include "timing.h"
#include "util.h"

NEXTPNR_NAMESPACE_BEGIN

class SAPlacer
{
  private:
    struct BoundingBox
    {
        // Actual bounding box
        int x0 = 0, x1 = 0, y0 = 0, y1 = 0;
        // Number of cells at each extremity
        int nx0 = 0, nx1 = 0, ny0 = 0, ny1 = 0;
        wirelen_t hpwl(const Placer1Cfg &cfg) const
        {
            return wirelen_t(cfg.hpwl_scale_x * (x1 - x0) + cfg.hpwl_scale_y * (y1 - y0));
        }
    };

  public:
    SAPlacer(Context *ctx, Placer1Cfg cfg)
            : ctx(ctx), fast_bels(ctx, /*check_bel_available=*/false, cfg.minBelsForGridPick), cfg(cfg), tmg(ctx)
    {
        for (auto bel : ctx->getBels()) {
            Loc loc = ctx->getBelLocation(bel);
            max_x = std::max(max_x, loc.x);
            max_y = std::max(max_y, loc.y);
        }
        diameter = std::max(max_x, max_y) + 1;

        pool<IdString> cell_types_in_use;
        for (auto &cell : ctx->cells) {
            IdString cell_type = cell.second->type;
            cell_types_in_use.insert(cell_type);
        }

        for (auto cell_type : cell_types_in_use) {
            fast_bels.addCellType(cell_type);
        }

        net_bounds.resize(ctx->nets.size());
        net_arc_tcost.resize(ctx->nets.size());
        old_udata.reserve(ctx->nets.size());
        net_by_udata.reserve(ctx->nets.size());
        decltype(NetInfo::udata) n = 0;
        for (auto &net : ctx->nets) {
            old_udata.emplace_back(net.second->udata);
            net_arc_tcost.at(n).resize(net.second->users.size());
            net.second->udata = n++;
            net_by_udata.push_back(net.second.get());
        }
        for (auto &region : ctx->region) {
            Region *r = region.second.get();
            BoundingBox bb;
            if (r->constr_bels) {
                bb.x0 = std::numeric_limits<int>::max();
                bb.x1 = std::numeric_limits<int>::min();
                bb.y0 = std::numeric_limits<int>::max();
                bb.y1 = std::numeric_limits<int>::min();
                for (auto bel : r->bels) {
                    Loc loc = ctx->getBelLocation(bel);
                    bb.x0 = std::min(bb.x0, loc.x);
                    bb.x1 = std::max(bb.x1, loc.x);
                    bb.y0 = std::min(bb.y0, loc.y);
                    bb.y1 = std::max(bb.y1, loc.y);
                }
            } else {
                bb.x0 = 0;
                bb.y0 = 0;
                bb.x1 = max_x;
                bb.y1 = max_y;
            }
            region_bounds[r->name] = bb;
        }
        build_port_index();
        for (auto &cell : ctx->cells) {
            CellInfo *ci = cell.second.get();
            if (ci->cluster == ClusterId())
                continue;
            cluster2cell[ci->cluster].push_back(ci);
        }
    }

    ~SAPlacer()
    {
        for (auto &net : ctx->nets)
            net.second->udata = old_udata[net.second->udata];
    }

    bool place(bool refine = false)
    {
        log_break();

        ScopeLock<Context> lock(ctx);

        size_t placed_cells = 0;
        std::vector<CellInfo *> autoplaced;
        std::vector<CellInfo *> chain_basis;
        if (!refine) {
            // Initial constraints placer
            for (auto &cell_entry : ctx->cells) {
                CellInfo *cell = cell_entry.second.get();
                auto loc = cell->attrs.find(ctx->id("BEL"));
                if (loc != cell->attrs.end()) {
                    std::string loc_name = loc->second.as_string();
                    BelId bel = ctx->getBelByNameStr(loc_name);
                    if (bel == BelId()) {
                        log_error("No Bel named \'%s\' located for "
                                  "this chip (processing BEL attribute on \'%s\')\n",
                                  loc_name.c_str(), cell->name.c_str(ctx));
                    }

                    if (!ctx->isValidBelForCellType(cell->type, bel)) {
                        IdString bel_type = ctx->getBelType(bel);
                        log_error("Bel \'%s\' of type \'%s\' does not match cell "
                                  "\'%s\' of type \'%s\'\n",
                                  loc_name.c_str(), bel_type.c_str(ctx), cell->name.c_str(ctx), cell->type.c_str(ctx));
                    }
                    auto bound_cell = ctx->getBoundBelCell(bel);
                    if (bound_cell) {
                        log_error(
                                "Cell \'%s\' cannot be bound to bel \'%s\' since it is already bound to cell \'%s\'\n",
                                cell->name.c_str(ctx), loc_name.c_str(), bound_cell->name.c_str(ctx));
                    }

                    ctx->bindBel(bel, cell, STRENGTH_USER);
                    if (!ctx->isBelLocationValid(bel)) {
                        IdString bel_type = ctx->getBelType(bel);
                        log_error("Bel \'%s\' of type \'%s\' is not valid for cell "
                                  "\'%s\' of type \'%s\'\n",
                                  loc_name.c_str(), bel_type.c_str(ctx), cell->name.c_str(ctx), cell->type.c_str(ctx));
                    }
                    locked_bels.insert(bel);
                    placed_cells++;
                }
            }
            int constr_placed_cells = placed_cells;
            log_info("Placed %d cells based on constraints.\n", int(placed_cells));
            ctx->yield();

            // Sort to-place cells for deterministic initial placement

            for (auto &cell : ctx->cells) {
                CellInfo *ci = cell.second.get();
                if (ci->bel == BelId()) {
                    autoplaced.push_back(cell.second.get());
                }
            }
            std::sort(autoplaced.begin(), autoplaced.end(), [](CellInfo *a, CellInfo *b) { return a->name < b->name; });
            ctx->shuffle(autoplaced);
            auto iplace_start = std::chrono::high_resolution_clock::now();
            // Place cells randomly initially
            log_info("Creating initial placement for remaining %d cells.\n", int(autoplaced.size()));

            for (auto cell : autoplaced) {
                place_initial(cell);
                placed_cells++;
                if ((placed_cells - constr_placed_cells) % 500 == 0)
                    log_info("  initial placement placed %d/%d cells\n", int(placed_cells - constr_placed_cells),
                             int(autoplaced.size()));
            }
            if ((placed_cells - constr_placed_cells) % 500 != 0)
                log_info("  initial placement placed %d/%d cells\n", int(placed_cells - constr_placed_cells),
                         int(autoplaced.size()));
            if (cfg.budgetBased && cfg.slack_redist_iter > 0)
                assign_budget(ctx);
            ctx->yield();
            auto iplace_end = std::chrono::high_resolution_clock::now();
            log_info("Initial placement time %.02fs\n",
                     std::chrono::duration<float>(iplace_end - iplace_start).count());
            log_info("Running simulated annealing placer.\n");
        } else {
            for (auto &cell : ctx->cells) {
                CellInfo *ci = cell.second.get();
                if (ci->belStrength > STRENGTH_STRONG) {
                    continue;
                } else if (ci->cluster != ClusterId()) {
                    if (ctx->getClusterRootCell(ci->cluster) == ci)
                        chain_basis.push_back(ci);
                    else
                        continue;
                } else {
                    autoplaced.push_back(ci);
                }
            }
            require_legal = false;
            diameter = 3;
            log_info("Running simulated annealing placer for refinement.\n");
        }
        auto saplace_start = std::chrono::high_resolution_clock::now();

        // Invoke timing analysis to obtain criticalities
        tmg.setup_only = true;
        if (!cfg.budgetBased)
            tmg.setup();

        // Calculate costs after initial placement
        setup_costs();
        moveChange.init(this);
        curr_wirelen_cost = total_wirelen_cost();
        curr_timing_cost = total_timing_cost();
        last_wirelen_cost = curr_wirelen_cost;
        last_timing_cost = curr_timing_cost;

        if (cfg.netShareWeight > 0)
            setup_nets_by_tile();

        wirelen_t avg_wirelen = curr_wirelen_cost;
        wirelen_t min_wirelen = curr_wirelen_cost;

        int n_no_progress = 0;
        temp = refine ? 1e-7 : cfg.startTemp;

        // Main simulated annealing loop
        for (int iter = 1;; iter++) {
            n_move = n_accept = 0;
            improved = false;

            if (iter % 5 == 0 || iter == 1)
                log_info("  at iteration #%d: temp = %f, timing cost = "
                         "%.0f, wirelen = %.0f\n",
                         iter, temp, double(curr_timing_cost), double(curr_wirelen_cost));

            for (int m = 0; m < 15; ++m) {
                // Loop through all automatically placed cells
                for (auto cell : autoplaced) {
                    // Find another random Bel for this cell
                    BelId try_bel = random_bel_for_cell(cell);
                    // If valid, try and swap to a new position and see if
                    // the new position is valid/worthwhile
                    if (try_bel != BelId() && try_bel != cell->bel)
                        try_swap_position(cell, try_bel);
                }
                // Also try swapping chains, if applicable
                for (auto cb : chain_basis) {
                    Loc chain_base_loc = ctx->getBelLocation(cb->bel);
                    BelId try_base = random_bel_for_cell(cb, chain_base_loc.z);
                    if (try_base != BelId() && try_base != cb->bel)
                        try_swap_chain(cb, try_base);
                }
            }

            if (ctx->debug) {
                // Verify correctness of incremental wirelen updates
                for (size_t i = 0; i < net_bounds.size(); i++) {
                    auto net = net_by_udata[i];
                    if (ignore_net(net))
                        continue;
                    auto &incr = net_bounds.at(i), gold = get_net_bounds(net);
                    NPNR_ASSERT(incr.x0 == gold.x0);
                    NPNR_ASSERT(incr.x1 == gold.x1);
                    NPNR_ASSERT(incr.y0 == gold.y0);
                    NPNR_ASSERT(incr.y1 == gold.y1);
                    NPNR_ASSERT(incr.nx0 == gold.nx0);
                    NPNR_ASSERT(incr.nx1 == gold.nx1);
                    NPNR_ASSERT(incr.ny0 == gold.ny0);
                    NPNR_ASSERT(incr.ny1 == gold.ny1);
                }
            }

            if (curr_wirelen_cost < min_wirelen) {
                min_wirelen = curr_wirelen_cost;
                improved = true;
            }

            // Heuristic to improve placement on the 8k
            if (improved)
                n_no_progress = 0;
            else
                n_no_progress++;

            if (temp <= 1e-7 && n_no_progress >= (refine ? 1 : 5)) {
                log_info("  at iteration #%d: temp = %f, timing cost = "
                         "%.0f, wirelen = %.0f \n",
                         iter, temp, double(curr_timing_cost), double(curr_wirelen_cost));
                break;
            }

            double Raccept = double(n_accept) / double(n_move);

            int M = std::max(max_x, max_y) + 1;

            if (ctx->verbose)
                log("iter #%d: temp = %f, timing cost = "
                    "%.0f, wirelen = %.0f, dia = %d, Ra = %.02f \n",
                    iter, temp, double(curr_timing_cost), double(curr_wirelen_cost), diameter, Raccept);

            if (curr_wirelen_cost < 0.95 * avg_wirelen && curr_wirelen_cost > 0) {
                avg_wirelen = 0.8 * avg_wirelen + 0.2 * curr_wirelen_cost;
            } else {
                double diam_next = diameter * (1.0 - 0.44 + Raccept);
                diameter = std::max<int>(1, std::min<int>(M, int(diam_next + 0.5)));
                if (Raccept > 0.96) {
                    temp *= 0.5;
                } else if (Raccept > 0.8) {
                    temp *= 0.9;
                } else if (Raccept > 0.15 && diameter > 1) {
                    temp *= 0.95;
                } else {
                    temp *= 0.8;
                }
            }
            // Once cooled below legalise threshold, run legalisation and start requiring
            // legal moves only
            if (diameter < legalise_dia && require_legal) {
                if (legalise_relative_constraints(ctx)) {
                    // Only increase temperature if something was moved
                    autoplaced.clear();
                    chain_basis.clear();
                    for (auto &cell : ctx->cells) {
                        if (cell.second->belStrength <= STRENGTH_STRONG && cell.second->cluster != ClusterId() &&
                            ctx->getClusterRootCell(cell.second->cluster) == cell.second.get())
                            chain_basis.push_back(cell.second.get());
                        else if (cell.second->belStrength < STRENGTH_STRONG)
                            autoplaced.push_back(cell.second.get());
                    }
                    // temp = post_legalise_temp;
                    // diameter = std::min<int>(M, diameter * post_legalise_dia_scale);
                    ctx->shuffle(autoplaced);

                    // Legalisation is a big change so force a slack redistribution here
                    if (cfg.slack_redist_iter > 0 && cfg.budgetBased)
                        assign_budget(ctx, true /* quiet */);
                }
                require_legal = false;
            } else if (cfg.budgetBased && cfg.slack_redist_iter > 0 && iter % cfg.slack_redist_iter == 0) {
                assign_budget(ctx, true /* quiet */);
            }

            // Invoke timing analysis to obtain criticalities
            if (!cfg.budgetBased && cfg.timing_driven)
                tmg.run();
            // Need to rebuild costs after criticalities change
            setup_costs();
            // Reset incremental bounds
            moveChange.reset(this);
            moveChange.new_net_bounds = net_bounds;

            // Recalculate total metric entirely to avoid rounding errors
            // accumulating over time
            curr_wirelen_cost = total_wirelen_cost();
            curr_timing_cost = total_timing_cost();
            last_wirelen_cost = curr_wirelen_cost;
            last_timing_cost = curr_timing_cost;
            // Let the UI show visualization updates.
            ctx->yield();
        }

        auto saplace_end = std::chrono::high_resolution_clock::now();
        log_info("SA placement time %.02fs\n", std::chrono::duration<float>(saplace_end - saplace_start).count());

        // Final post-placement validity check
        ctx->yield();
        for (auto bel : ctx->getBels()) {
            CellInfo *cell = ctx->getBoundBelCell(bel);
            if (!ctx->isBelLocationValid(bel)) {
                std::string cell_text = "no cell";
                if (cell != nullptr)
                    cell_text = std::string("cell '") + ctx->nameOf(cell) + "'";
                if (ctx->force) {
                    log_warning("post-placement validity check failed for Bel '%s' "
                                "(%s)\n",
                                ctx->nameOfBel(bel), cell_text.c_str());
                } else {
                    log_error("post-placement validity check failed for Bel '%s' "
                              "(%s)\n",
                              ctx->nameOfBel(bel), cell_text.c_str());
                }
            }
        }
        timing_analysis(ctx);

        return true;
    }

  private:
    // Initial random placement
    void place_initial(CellInfo *cell)
    {
        bool all_placed = false;
        int iters = 25;
        while (!all_placed) {
            BelId best_bel = BelId();
            uint64_t best_score = std::numeric_limits<uint64_t>::max(),
                     best_ripup_score = std::numeric_limits<uint64_t>::max();
            CellInfo *ripup_target = nullptr;
            BelId ripup_bel = BelId();
            if (cell->bel != BelId()) {
                ctx->unbindBel(cell->bel);
            }
            IdString targetType = cell->type;

            auto proc_bel = [&](BelId bel) {
                if (ctx->isValidBelForCellType(targetType, bel)) {
                    if (ctx->checkBelAvail(bel)) {
                        uint64_t score = ctx->rng64();
                        if (score <= best_score) {
                            best_score = score;
                            best_bel = bel;
                        }
                    } else {
                        uint64_t score = ctx->rng64();
                        CellInfo *bound_cell = ctx->getBoundBelCell(bel);
                        if (score <= best_ripup_score && bound_cell->belStrength < STRENGTH_STRONG) {
                            best_ripup_score = score;
                            ripup_target = bound_cell;
                            ripup_bel = bel;
                        }
                    }
                }
            };

            if (cell->region != nullptr && cell->region->constr_bels) {
                for (auto bel : cell->region->bels) {
                    proc_bel(bel);
                }
            } else {
                for (auto bel : ctx->getBels()) {
                    proc_bel(bel);
                }
            }

            if (best_bel == BelId()) {
                if (iters == 0 || ripup_bel == BelId())
                    log_error("failed to place cell '%s' of type '%s'\n", cell->name.c_str(ctx), cell->type.c_str(ctx));
                --iters;
                ctx->unbindBel(ripup_target->bel);
                best_bel = ripup_bel;
            } else {
                ripup_target = nullptr;
                all_placed = true;
            }
            ctx->bindBel(best_bel, cell, STRENGTH_WEAK);

            if (!ctx->isBelLocationValid(best_bel)) {
                ctx->unbindBel(best_bel);
                if (ripup_target != nullptr) {
                    ctx->bindBel(best_bel, ripup_target, STRENGTH_WEAK);
                }
                all_placed = false;
                continue;
            }

            // Back annotate location
            cell->attrs[ctx->id("BEL")] = ctx->getBelName(cell->bel).str(ctx);
            cell = ripup_target;
        }
    }

    // Attempt a SA position swap, return true on success or false on failure
    bool try_swap_position(CellInfo *cell, BelId newBel)
    {
        static const double epsilon = 1e-20;
        moveChange.reset(this);
        if (!require_legal && cell->cluster != ClusterId())
            return false;
        BelId oldBel = cell->bel;
        CellInfo *other_cell = ctx->getBoundBelCell(newBel);
        if (!require_legal && other_cell != nullptr &&
            (other_cell->cluster != ClusterId() || other_cell->belStrength > STRENGTH_WEAK)) {
            return false;
        }
        int old_dist = get_constraints_distance(ctx, cell);
        int new_dist;
        if (other_cell != nullptr)
            old_dist += get_constraints_distance(ctx, other_cell);
        double delta = 0;

        if (!ctx->isValidBelForCellType(cell->type, newBel)) {
            return false;
        }
        if (other_cell != nullptr && !ctx->isValidBelForCellType(other_cell->type, oldBel)) {
            return false;
        }

        int net_delta_score = 0;
        if (cfg.netShareWeight > 0)
            net_delta_score += update_nets_by_tile(cell, ctx->getBelLocation(cell->bel), ctx->getBelLocation(newBel));

        ctx->unbindBel(oldBel);
        if (other_cell != nullptr) {
            ctx->unbindBel(newBel);
        }

        ctx->bindBel(newBel, cell, STRENGTH_WEAK);

        if (other_cell != nullptr) {
            ctx->bindBel(oldBel, other_cell, STRENGTH_WEAK);
            if (cfg.netShareWeight > 0)
                net_delta_score +=
                        update_nets_by_tile(other_cell, ctx->getBelLocation(newBel), ctx->getBelLocation(oldBel));
        }

        add_move_cell(moveChange, cell, oldBel);

        if (other_cell != nullptr) {
            add_move_cell(moveChange, other_cell, newBel);
        }

        // Always check both the new and old locations; as in some cases of dedicated routing ripping up a cell can deny
        // use of a dedicated path and thus make a site illegal
        if (!ctx->isBelLocationValid(newBel) || !ctx->isBelLocationValid(oldBel)) {
            ctx->unbindBel(newBel);
            if (other_cell != nullptr)
                ctx->unbindBel(oldBel);
            goto swap_fail;
        }

        // Recalculate metrics for all nets touched by the perturbation
        compute_cost_changes(moveChange);

        new_dist = get_constraints_distance(ctx, cell);
        if (other_cell != nullptr)
            new_dist += get_constraints_distance(ctx, other_cell);
        delta = lambda * (moveChange.timing_delta / std::max<double>(last_timing_cost, epsilon)) +
                (1 - lambda) * (double(moveChange.wirelen_delta) / std::max<double>(last_wirelen_cost, epsilon));
        delta += (cfg.constraintWeight / temp) * (new_dist - old_dist) / last_wirelen_cost;
        if (cfg.netShareWeight > 0)
            delta += -cfg.netShareWeight * (net_delta_score / std::max<double>(total_net_share, epsilon));
        n_move++;
        // SA acceptance criteria
        if (delta < 0 || (temp > 1e-8 && (ctx->rng() / float(0x3fffffff)) <= std::exp(-delta / temp))) {
            n_accept++;
        } else {
            if (other_cell != nullptr)
                ctx->unbindBel(oldBel);
            ctx->unbindBel(newBel);
            goto swap_fail;
        }
        commit_cost_changes(moveChange);
#if 0
        log_info("swap %s -> %s\n", cell->name.c_str(ctx), ctx->nameOfBel(newBel));
        if (other_cell != nullptr)
            log_info("swap %s -> %s\n", other_cell->name.c_str(ctx), ctx->nameOfBel(oldBel));
#endif
        return true;
    swap_fail:
        ctx->bindBel(oldBel, cell, STRENGTH_WEAK);
        if (other_cell != nullptr) {
            ctx->bindBel(newBel, other_cell, STRENGTH_WEAK);
            if (cfg.netShareWeight > 0)
                update_nets_by_tile(other_cell, ctx->getBelLocation(oldBel), ctx->getBelLocation(newBel));
        }
        if (cfg.netShareWeight > 0)
            update_nets_by_tile(cell, ctx->getBelLocation(newBel), ctx->getBelLocation(oldBel));
        return false;
    }

    // Swap the Bel of a cell with another, return the original location
    BelId swap_cell_bels(CellInfo *cell, BelId newBel)
    {
        BelId oldBel = cell->bel;
#if 0
        log_info("%s old: %s new: %s\n", cell->name.c_str(ctx), ctx->nameOfBel(cell->bel), ctx->nameOfBel(newBel));
#endif
        CellInfo *bound = ctx->getBoundBelCell(newBel);
        if (bound != nullptr)
            ctx->unbindBel(newBel);
        ctx->unbindBel(oldBel);
        ctx->bindBel(newBel, cell, (cell->cluster != ClusterId()) ? STRENGTH_STRONG : STRENGTH_WEAK);
        if (bound != nullptr) {
            ctx->bindBel(oldBel, bound, (bound->cluster != ClusterId()) ? STRENGTH_STRONG : STRENGTH_WEAK);
            if (cfg.netShareWeight > 0)
                update_nets_by_tile(bound, ctx->getBelLocation(newBel), ctx->getBelLocation(oldBel));
        }
        if (cfg.netShareWeight > 0)
            update_nets_by_tile(cell, ctx->getBelLocation(oldBel), ctx->getBelLocation(newBel));
        return oldBel;
    }

    // Attempt to swap a chain with a non-chain
    bool try_swap_chain(CellInfo *cell, BelId newBase)
    {
        std::vector<std::pair<CellInfo *, Loc>> cell_rel;
        dict<IdString, BelId> moved_cells;
        double delta = 0;
        int orig_share_cost = total_net_share;
        moveChange.reset(this);
#if CHAIN_DEBUG
        log_info("finding cells for chain swap %s\n", cell->name.c_str(ctx));
#endif
        std::queue<std::pair<ClusterId, BelId>> displaced_clusters;
        displaced_clusters.emplace(cell->cluster, newBase);
        while (!displaced_clusters.empty()) {
            std::vector<std::pair<CellInfo *, BelId>> dest_bels;
            auto cursor = displaced_clusters.front();
#if CHAIN_DEBUG
            log_info("%d Cluster %s\n", __LINE__, cursor.first.c_str(ctx));
#endif
            displaced_clusters.pop();
            if (!ctx->getClusterPlacement(cursor.first, cursor.second, dest_bels))
                goto swap_fail;
            for (const auto &db : dest_bels) {
                // Ensure the cluster is ripped up
                if (db.first->bel != BelId()) {
                    moved_cells[db.first->name] = db.first->bel;
#if CHAIN_DEBUG
                    log_info("%d unbind %s\n", __LINE__, ctx->nameOfBel(db.first->bel));
#endif
                    ctx->unbindBel(db.first->bel);
                }
            }
            for (const auto &db : dest_bels) {
                CellInfo *bound = ctx->getBoundBelCell(db.second);
                BelId old_bel = moved_cells.at(db.first->name);
                if (!ctx->checkBelAvail(old_bel) && bound != nullptr) {
                    // Simple swap no longer possible
                    goto swap_fail;
                }
                if (bound != nullptr) {
                    if (moved_cells.count(bound->name)) {
                        // Don't move a cell multiple times in the same go
                        goto swap_fail;
                    } else if (bound->belStrength > STRENGTH_STRONG) {
                        goto swap_fail;
                    } else if (bound->cluster != ClusterId()) {
                        // Displace the entire cluster
                        Loc old_loc = ctx->getBelLocation(old_bel);
                        Loc bound_loc = ctx->getBelLocation(bound->bel);
                        Loc root_loc = ctx->getBelLocation(ctx->getClusterRootCell(bound->cluster)->bel);
                        BelId new_root = ctx->getBelByLocation(Loc(old_loc.x + (root_loc.x - bound_loc.x),
                                                                   old_loc.y + (root_loc.y - bound_loc.y),
                                                                   old_loc.z + (root_loc.z - bound_loc.z)));
                        if (new_root == BelId())
                            goto swap_fail;
                        for (auto cluster_cell : cluster2cell.at(bound->cluster)) {
                            moved_cells[cluster_cell->name] = cluster_cell->bel;
#if CHAIN_DEBUG
                            log_info("%d unbind %s\n", __LINE__, ctx->nameOfBel(cluster_cell->bel));
#endif
                            ctx->unbindBel(cluster_cell->bel);
                        }
                        displaced_clusters.emplace(bound->cluster, new_root);
                    } else {
                        // Just a single cell to move
                        moved_cells[bound->name] = bound->bel;
#if CHAIN_DEBUG
                        log_info("%d unbind %s\n", __LINE__, ctx->nameOfBel(bound->bel));
                        log_info("%d bind %s %s\n", __LINE__, ctx->nameOfBel(old_bel), ctx->nameOf(bound));
#endif
                        ctx->unbindBel(bound->bel);
                        ctx->bindBel(old_bel, bound, STRENGTH_WEAK);
                    }
                } else if (!ctx->checkBelAvail(db.second)) {
                    goto swap_fail;
                }
                // All those shenanigans should now mean the target bel is free to use
#if CHAIN_DEBUG
                log_info("%d bind %s %s\n", __LINE__, ctx->nameOfBel(db.second), ctx->nameOf(db.first));
#endif
                ctx->bindBel(db.second, db.first, STRENGTH_WEAK);
            }
        }

        for (const auto &mm : moved_cells) {
            CellInfo *cell = ctx->cells.at(mm.first).get();
            add_move_cell(moveChange, cell, moved_cells.at(cell->name));
            if (cfg.netShareWeight > 0)
                update_nets_by_tile(cell, ctx->getBelLocation(moved_cells.at(cell->name)),
                                    ctx->getBelLocation(cell->bel));
            if (!ctx->isBelLocationValid(cell->bel) || !cell->testRegion(cell->bel))
                goto swap_fail;
        }
#if CHAIN_DEBUG
        log_info("legal chain swap %s\n", cell->name.c_str(ctx));
#endif
        compute_cost_changes(moveChange);
        delta = lambda * (moveChange.timing_delta / last_timing_cost) +
                (1 - lambda) * (double(moveChange.wirelen_delta) / last_wirelen_cost);
        if (cfg.netShareWeight > 0) {
            delta +=
                    cfg.netShareWeight * (orig_share_cost - total_net_share) / std::max<double>(total_net_share, 1e-20);
        }
        n_move++;
        // SA acceptance criteria
        if (delta < 0 || (temp > 1e-8 && (ctx->rng() / float(0x3fffffff)) <= std::exp(-delta / temp))) {
            n_accept++;
#if CHAIN_DEBUG
            log_info("accepted chain swap %s\n", cell->name.c_str(ctx));
#endif
        } else {
            goto swap_fail;
        }
        commit_cost_changes(moveChange);
        return true;
    swap_fail:
#if CHAIN_DEBUG
        log_info("Swap failed\n");
#endif
        for (auto cell_pair : moved_cells) {
            CellInfo *cell = ctx->cells.at(cell_pair.first).get();
            if (cell->bel != BelId()) {
#if CHAIN_DEBUG
                log_info("%d unbind %s\n", __LINE__, ctx->nameOfBel(cell->bel));
#endif
                ctx->unbindBel(cell->bel);
            }
        }
        for (auto cell_pair : moved_cells) {
            CellInfo *cell = ctx->cells.at(cell_pair.first).get();
#if CHAIN_DEBUG
            log_info("%d bind %s %s\n", __LINE__, ctx->nameOfBel(cell_pair.second), cell->name.c_str(ctx));
#endif
            ctx->bindBel(cell_pair.second, cell, STRENGTH_WEAK);
        }
        return false;
    }

    // Find a random Bel of the correct type for a cell, within the specified
    // diameter
    BelId random_bel_for_cell(CellInfo *cell, int force_z = -1)
    {
        IdString targetType = cell->type;
        Loc curr_loc = ctx->getBelLocation(cell->bel);
        int count = 0;

        int dx = diameter, dy = diameter;
        if (cell->region != nullptr && cell->region->constr_bels) {
            dx = std::min(cfg.hpwl_scale_x * diameter,
                          (region_bounds[cell->region->name].x1 - region_bounds[cell->region->name].x0) + 1);
            dy = std::min(cfg.hpwl_scale_y * diameter,
                          (region_bounds[cell->region->name].y1 - region_bounds[cell->region->name].y0) + 1);
            // Clamp location to within bounds
            curr_loc.x = std::max(region_bounds[cell->region->name].x0, curr_loc.x);
            curr_loc.x = std::min(region_bounds[cell->region->name].x1, curr_loc.x);
            curr_loc.y = std::max(region_bounds[cell->region->name].y0, curr_loc.y);
            curr_loc.y = std::min(region_bounds[cell->region->name].y1, curr_loc.y);
        }

        FastBels::FastBelsData *bel_data;
        auto type_cnt = fast_bels.getBelsForCellType(targetType, &bel_data);

        while (true) {
            int nx = ctx->rng(2 * dx + 1) + std::max(curr_loc.x - dx, 0);
            int ny = ctx->rng(2 * dy + 1) + std::max(curr_loc.y - dy, 0);
            if (cfg.minBelsForGridPick >= 0 && type_cnt < cfg.minBelsForGridPick)
                nx = ny = 0;
            if (nx >= int(bel_data->size()))
                continue;
            if (ny >= int(bel_data->at(nx).size()))
                continue;
            const auto &fb = bel_data->at(nx).at(ny);
            if (fb.size() == 0)
                continue;
            BelId bel = fb.at(ctx->rng(int(fb.size())));
            if (force_z != -1) {
                Loc loc = ctx->getBelLocation(bel);
                if (loc.z != force_z)
                    continue;
            }
            if (!cell->testRegion(bel))
                continue;
            if (locked_bels.find(bel) != locked_bels.end())
                continue;
            count++;
            return bel;
        }
    }

    // Return true if a net is to be entirely ignored
    inline bool ignore_net(NetInfo *net)
    {
        return net->driver.cell == nullptr || net->driver.cell->bel == BelId() ||
               ctx->getBelGlobalBuf(net->driver.cell->bel);
    }

    // Get the bounding box for a net
    inline BoundingBox get_net_bounds(NetInfo *net)
    {
        BoundingBox bb;
        NPNR_ASSERT(net->driver.cell != nullptr);
        Loc dloc = ctx->getBelLocation(net->driver.cell->bel);
        bb.x0 = dloc.x;
        bb.x1 = dloc.x;
        bb.y0 = dloc.y;
        bb.y1 = dloc.y;
        bb.nx0 = 1;
        bb.nx1 = 1;
        bb.ny0 = 1;
        bb.ny1 = 1;
        for (auto user : net->users) {
            if (user.cell->bel == BelId())
                continue;
            Loc uloc = ctx->getBelLocation(user.cell->bel);
            if (bb.x0 == uloc.x)
                ++bb.nx0;
            else if (uloc.x < bb.x0) {
                bb.x0 = uloc.x;
                bb.nx0 = 1;
            }
            if (bb.x1 == uloc.x)
                ++bb.nx1;
            else if (uloc.x > bb.x1) {
                bb.x1 = uloc.x;
                bb.nx1 = 1;
            }
            if (bb.y0 == uloc.y)
                ++bb.ny0;
            else if (uloc.y < bb.y0) {
                bb.y0 = uloc.y;
                bb.ny0 = 1;
            }
            if (bb.y1 == uloc.y)
                ++bb.ny1;
            else if (uloc.y > bb.y1) {
                bb.y1 = uloc.y;
                bb.ny1 = 1;
            }
        }

        return bb;
    }

    // Get the timing cost for an arc of a net
    inline double get_timing_cost(NetInfo *net, size_t user)
    {
        int cc;
        if (net->driver.cell == nullptr)
            return 0;
        if (ctx->getPortTimingClass(net->driver.cell, net->driver.port, cc) == TMG_IGNORE)
            return 0;
        if (cfg.budgetBased) {
            double delay = ctx->getDelayNS(ctx->predictArcDelay(net, net->users.at(user)));
            return std::min(10.0, std::exp(delay - ctx->getDelayNS(net->users.at(user).budget) / 10));
        } else {
            float crit = tmg.get_criticality(CellPortKey(net->users.at(user)));
            double delay = ctx->getDelayNS(ctx->predictArcDelay(net, net->users.at(user)));
            return delay * std::pow(crit, crit_exp);
        }
    }

    // Set up the cost maps
    void setup_costs()
    {
        for (auto &net : ctx->nets) {
            NetInfo *ni = net.second.get();
            if (ignore_net(ni))
                continue;
            net_bounds[ni->udata] = get_net_bounds(ni);
            if (cfg.timing_driven && int(ni->users.size()) < cfg.timingFanoutThresh)
                for (size_t i = 0; i < ni->users.size(); i++)
                    net_arc_tcost[ni->udata][i] = get_timing_cost(ni, i);
        }
    }

    // Get the total wiring cost for the design
    wirelen_t total_wirelen_cost()
    {
        wirelen_t cost = 0;
        for (const auto &net : net_bounds)
            cost += net.hpwl(cfg);
        return cost;
    }

    // Get the total timing cost for the design
    double total_timing_cost()
    {
        double cost = 0;
        for (const auto &net : net_arc_tcost) {
            for (auto arc_cost : net) {
                cost += arc_cost;
            }
        }
        return cost;
    }

    // Cost-change-related data for a move
    struct MoveChangeData
    {

        enum BoundChangeType
        {
            NO_CHANGE,
            CELL_MOVED_INWARDS,
            CELL_MOVED_OUTWARDS,
            FULL_RECOMPUTE
        };

        std::vector<decltype(NetInfo::udata)> bounds_changed_nets_x, bounds_changed_nets_y;
        std::vector<std::pair<decltype(NetInfo::udata), size_t>> changed_arcs;

        std::vector<BoundChangeType> already_bounds_changed_x, already_bounds_changed_y;
        std::vector<std::vector<bool>> already_changed_arcs;

        std::vector<BoundingBox> new_net_bounds;
        std::vector<std::pair<std::pair<decltype(NetInfo::udata), size_t>, double>> new_arc_costs;

        wirelen_t wirelen_delta = 0;
        double timing_delta = 0;

        void init(SAPlacer *p)
        {
            already_bounds_changed_x.resize(p->ctx->nets.size());
            already_bounds_changed_y.resize(p->ctx->nets.size());
            already_changed_arcs.resize(p->ctx->nets.size());
            for (auto &net : p->ctx->nets) {
                already_changed_arcs.at(net.second->udata).resize(net.second->users.size());
            }
            new_net_bounds = p->net_bounds;
        }

        void reset(SAPlacer *p)
        {
            for (auto bc : bounds_changed_nets_x) {
                new_net_bounds[bc] = p->net_bounds[bc];
                already_bounds_changed_x[bc] = NO_CHANGE;
            }
            for (auto bc : bounds_changed_nets_y) {
                new_net_bounds[bc] = p->net_bounds[bc];
                already_bounds_changed_y[bc] = NO_CHANGE;
            }
            for (const auto &tc : changed_arcs)
                already_changed_arcs[tc.first][tc.second] = false;
            bounds_changed_nets_x.clear();
            bounds_changed_nets_y.clear();
            changed_arcs.clear();
            new_arc_costs.clear();
            wirelen_delta = 0;
            timing_delta = 0;
        }

    } moveChange;

    void add_move_cell(MoveChangeData &mc, CellInfo *cell, BelId old_bel)
    {
        Loc curr_loc = ctx->getBelLocation(cell->bel);
        Loc old_loc = ctx->getBelLocation(old_bel);
        // Check net bounds
        for (const auto &port : cell->ports) {
            NetInfo *pn = port.second.net;
            if (pn == nullptr)
                continue;
            if (ignore_net(pn))
                continue;
            BoundingBox &curr_bounds = mc.new_net_bounds[pn->udata];
            // Incremental bounding box updates
            // Note that everything other than full updates are applied immediately rather than being queued,
            // so further updates to the same net in the same move are dealt with correctly.
            // If a full update is already queued, this can be considered a no-op
            if (mc.already_bounds_changed_x[pn->udata] != MoveChangeData::FULL_RECOMPUTE) {
                // Bounds x0
                if (curr_loc.x < curr_bounds.x0) {
                    // Further out than current bounds x0
                    curr_bounds.x0 = curr_loc.x;
                    curr_bounds.nx0 = 1;
                    if (mc.already_bounds_changed_x[pn->udata] == MoveChangeData::NO_CHANGE) {
                        // Checking already_bounds_changed_x ensures that each net is only added once
                        // to bounds_changed_nets, lest we add its HPWL change multiple times skewing the
                        // overall cost change
                        mc.already_bounds_changed_x[pn->udata] = MoveChangeData::CELL_MOVED_OUTWARDS;
                        mc.bounds_changed_nets_x.push_back(pn->udata);
                    }
                } else if (curr_loc.x == curr_bounds.x0 && old_loc.x > curr_bounds.x0) {
                    curr_bounds.nx0++;
                    if (mc.already_bounds_changed_x[pn->udata] == MoveChangeData::NO_CHANGE) {
                        mc.already_bounds_changed_x[pn->udata] = MoveChangeData::CELL_MOVED_OUTWARDS;
                        mc.bounds_changed_nets_x.push_back(pn->udata);
                    }
                } else if (old_loc.x == curr_bounds.x0 && curr_loc.x > curr_bounds.x0) {
                    if (mc.already_bounds_changed_x[pn->udata] == MoveChangeData::NO_CHANGE)
                        mc.bounds_changed_nets_x.push_back(pn->udata);
                    if (curr_bounds.nx0 == 1) {
                        mc.already_bounds_changed_x[pn->udata] = MoveChangeData::FULL_RECOMPUTE;
                    } else {
                        curr_bounds.nx0--;
                        if (mc.already_bounds_changed_x[pn->udata] == MoveChangeData::NO_CHANGE)
                            mc.already_bounds_changed_x[pn->udata] = MoveChangeData::CELL_MOVED_INWARDS;
                    }
                }

                // Bounds x1
                if (curr_loc.x > curr_bounds.x1) {
                    // Further out than current bounds x1
                    curr_bounds.x1 = curr_loc.x;
                    curr_bounds.nx1 = 1;
                    if (mc.already_bounds_changed_x[pn->udata] == MoveChangeData::NO_CHANGE) {
                        // Checking already_bounds_changed_x ensures that each net is only added once
                        // to bounds_changed_nets, lest we add its HPWL change multiple times skewing the
                        // overall cost change
                        mc.already_bounds_changed_x[pn->udata] = MoveChangeData::CELL_MOVED_OUTWARDS;
                        mc.bounds_changed_nets_x.push_back(pn->udata);
                    }
                } else if (curr_loc.x == curr_bounds.x1 && old_loc.x < curr_bounds.x1) {
                    curr_bounds.nx1++;
                    if (mc.already_bounds_changed_x[pn->udata] == MoveChangeData::NO_CHANGE) {
                        mc.already_bounds_changed_x[pn->udata] = MoveChangeData::CELL_MOVED_OUTWARDS;
                        mc.bounds_changed_nets_x.push_back(pn->udata);
                    }
                } else if (old_loc.x == curr_bounds.x1 && curr_loc.x < curr_bounds.x1) {
                    if (mc.already_bounds_changed_x[pn->udata] == MoveChangeData::NO_CHANGE)
                        mc.bounds_changed_nets_x.push_back(pn->udata);
                    if (curr_bounds.nx1 == 1) {
                        mc.already_bounds_changed_x[pn->udata] = MoveChangeData::FULL_RECOMPUTE;
                    } else {
                        curr_bounds.nx1--;
                        if (mc.already_bounds_changed_x[pn->udata] == MoveChangeData::NO_CHANGE)
                            mc.already_bounds_changed_x[pn->udata] = MoveChangeData::CELL_MOVED_INWARDS;
                    }
                }
            }
            if (mc.already_bounds_changed_y[pn->udata] != MoveChangeData::FULL_RECOMPUTE) {
                // Bounds y0
                if (curr_loc.y < curr_bounds.y0) {
                    // Further out than current bounds y0
                    curr_bounds.y0 = curr_loc.y;
                    curr_bounds.ny0 = 1;
                    if (mc.already_bounds_changed_y[pn->udata] == MoveChangeData::NO_CHANGE) {
                        mc.already_bounds_changed_y[pn->udata] = MoveChangeData::CELL_MOVED_OUTWARDS;
                        mc.bounds_changed_nets_y.push_back(pn->udata);
                    }
                } else if (curr_loc.y == curr_bounds.y0 && old_loc.y > curr_bounds.y0) {
                    curr_bounds.ny0++;
                    if (mc.already_bounds_changed_y[pn->udata] == MoveChangeData::NO_CHANGE) {
                        mc.already_bounds_changed_y[pn->udata] = MoveChangeData::CELL_MOVED_OUTWARDS;
                        mc.bounds_changed_nets_y.push_back(pn->udata);
                    }
                } else if (old_loc.y == curr_bounds.y0 && curr_loc.y > curr_bounds.y0) {
                    if (mc.already_bounds_changed_y[pn->udata] == MoveChangeData::NO_CHANGE)
                        mc.bounds_changed_nets_y.push_back(pn->udata);
                    if (curr_bounds.ny0 == 1) {
                        mc.already_bounds_changed_y[pn->udata] = MoveChangeData::FULL_RECOMPUTE;
                    } else {
                        curr_bounds.ny0--;
                        if (mc.already_bounds_changed_y[pn->udata] == MoveChangeData::NO_CHANGE)
                            mc.already_bounds_changed_y[pn->udata] = MoveChangeData::CELL_MOVED_INWARDS;
                    }
                }

                // Bounds y1
                if (curr_loc.y > curr_bounds.y1) {
                    // Further out than current bounds y1
                    curr_bounds.y1 = curr_loc.y;
                    curr_bounds.ny1 = 1;
                    if (mc.already_bounds_changed_y[pn->udata] == MoveChangeData::NO_CHANGE) {
                        mc.already_bounds_changed_y[pn->udata] = MoveChangeData::CELL_MOVED_OUTWARDS;
                        mc.bounds_changed_nets_y.push_back(pn->udata);
                    }
                } else if (curr_loc.y == curr_bounds.y1 && old_loc.y < curr_bounds.y1) {
                    curr_bounds.ny1++;
                    if (mc.already_bounds_changed_y[pn->udata] == MoveChangeData::NO_CHANGE) {
                        mc.already_bounds_changed_y[pn->udata] = MoveChangeData::CELL_MOVED_OUTWARDS;
                        mc.bounds_changed_nets_y.push_back(pn->udata);
                    }
                } else if (old_loc.y == curr_bounds.y1 && curr_loc.y < curr_bounds.y1) {
                    if (mc.already_bounds_changed_y[pn->udata] == MoveChangeData::NO_CHANGE)
                        mc.bounds_changed_nets_y.push_back(pn->udata);
                    if (curr_bounds.ny1 == 1) {
                        mc.already_bounds_changed_y[pn->udata] = MoveChangeData::FULL_RECOMPUTE;
                    } else {
                        curr_bounds.ny1--;
                        if (mc.already_bounds_changed_y[pn->udata] == MoveChangeData::NO_CHANGE)
                            mc.already_bounds_changed_y[pn->udata] = MoveChangeData::CELL_MOVED_INWARDS;
                    }
                }
            }

            if (cfg.timing_driven && int(pn->users.size()) < cfg.timingFanoutThresh) {
                // Output ports - all arcs change timing
                if (port.second.type == PORT_OUT) {
                    int cc;
                    TimingPortClass cls = ctx->getPortTimingClass(cell, port.first, cc);
                    if (cls != TMG_IGNORE)
                        for (size_t i = 0; i < pn->users.size(); i++)
                            if (!mc.already_changed_arcs[pn->udata][i]) {
                                mc.changed_arcs.emplace_back(std::make_pair(pn->udata, i));
                                mc.already_changed_arcs[pn->udata][i] = true;
                            }
                } else if (port.second.type == PORT_IN) {
                    auto usr = fast_port_to_user.at(std::make_pair(cell->name, port.first));
                    if (!mc.already_changed_arcs[pn->udata][usr]) {
                        mc.changed_arcs.emplace_back(std::make_pair(pn->udata, usr));
                        mc.already_changed_arcs[pn->udata][usr] = true;
                    }
                }
            }
        }
    }

    void compute_cost_changes(MoveChangeData &md)
    {
        for (const auto &bc : md.bounds_changed_nets_x) {
            if (md.already_bounds_changed_x[bc] == MoveChangeData::FULL_RECOMPUTE)
                md.new_net_bounds[bc] = get_net_bounds(net_by_udata[bc]);
        }
        for (const auto &bc : md.bounds_changed_nets_y) {
            if (md.already_bounds_changed_x[bc] != MoveChangeData::FULL_RECOMPUTE &&
                md.already_bounds_changed_y[bc] == MoveChangeData::FULL_RECOMPUTE)
                md.new_net_bounds[bc] = get_net_bounds(net_by_udata[bc]);
        }

        for (const auto &bc : md.bounds_changed_nets_x)
            md.wirelen_delta += md.new_net_bounds[bc].hpwl(cfg) - net_bounds[bc].hpwl(cfg);
        for (const auto &bc : md.bounds_changed_nets_y)
            if (md.already_bounds_changed_x[bc] == MoveChangeData::NO_CHANGE)
                md.wirelen_delta += md.new_net_bounds[bc].hpwl(cfg) - net_bounds[bc].hpwl(cfg);

        if (cfg.timing_driven) {
            for (const auto &tc : md.changed_arcs) {
                double old_cost = net_arc_tcost.at(tc.first).at(tc.second);
                double new_cost = get_timing_cost(net_by_udata.at(tc.first), tc.second);
                md.new_arc_costs.emplace_back(std::make_pair(tc, new_cost));
                md.timing_delta += (new_cost - old_cost);
                md.already_changed_arcs[tc.first][tc.second] = false;
            }
        }
    }

    void commit_cost_changes(MoveChangeData &md)
    {
        for (const auto &bc : md.bounds_changed_nets_x)
            net_bounds[bc] = md.new_net_bounds[bc];
        for (const auto &bc : md.bounds_changed_nets_y)
            net_bounds[bc] = md.new_net_bounds[bc];
        for (const auto &tc : md.new_arc_costs)
            net_arc_tcost[tc.first.first].at(tc.first.second) = tc.second;
        curr_wirelen_cost += md.wirelen_delta;
        curr_timing_cost += md.timing_delta;
    }
    // Build the cell port -> user index
    void build_port_index()
    {
        for (auto &net : ctx->nets) {
            NetInfo *ni = net.second.get();
            for (size_t i = 0; i < ni->users.size(); i++) {
                auto &usr = ni->users.at(i);
                fast_port_to_user[std::make_pair(usr.cell->name, usr.port)] = i;
            }
        }
    }

    // Simple routeability driven placement
    const int large_cell_thresh = 50;
    int total_net_share = 0;
    std::vector<std::vector<dict<IdString, int>>> nets_by_tile;
    void setup_nets_by_tile()
    {
        total_net_share = 0;
        nets_by_tile.resize(max_x + 1, std::vector<dict<IdString, int>>(max_y + 1));
        for (auto &cell : ctx->cells) {
            CellInfo *ci = cell.second.get();
            if (int(ci->ports.size()) > large_cell_thresh)
                continue;
            Loc loc = ctx->getBelLocation(ci->bel);
            auto &nbt = nets_by_tile.at(loc.x).at(loc.y);
            for (const auto &port : ci->ports) {
                if (port.second.net == nullptr)
                    continue;
                if (port.second.net->driver.cell == nullptr || ctx->getBelGlobalBuf(port.second.net->driver.cell->bel))
                    continue;
                int &s = nbt[port.second.net->name];
                if (s > 0)
                    ++total_net_share;
                ++s;
            }
        }
    }

    int update_nets_by_tile(CellInfo *ci, Loc old_loc, Loc new_loc)
    {
        if (int(ci->ports.size()) > large_cell_thresh)
            return 0;
        int loss = 0, gain = 0;
        auto &nbt_old = nets_by_tile.at(old_loc.x).at(old_loc.y);
        auto &nbt_new = nets_by_tile.at(new_loc.x).at(new_loc.y);

        for (const auto &port : ci->ports) {
            if (port.second.net == nullptr)
                continue;
            if (port.second.net->driver.cell == nullptr || ctx->getBelGlobalBuf(port.second.net->driver.cell->bel))
                continue;
            int &o = nbt_old[port.second.net->name];
            --o;
            NPNR_ASSERT(o >= 0);
            if (o > 0)
                ++loss;
            int &n = nbt_new[port.second.net->name];
            if (n > 0)
                ++gain;
            ++n;
        }
        int delta = gain - loss;
        total_net_share += delta;
        return delta;
    }

    // Get the combined wirelen/timing metric
    inline double curr_metric()
    {
        return lambda * curr_timing_cost + (1 - lambda) * curr_wirelen_cost - cfg.netShareWeight * total_net_share;
    }

    // Map nets to their bounding box (so we can skip recompute for moves that do not exceed the bounds
    std::vector<BoundingBox> net_bounds;
    // Map net arcs to their timing cost (criticality * delay ns)
    std::vector<std::vector<double>> net_arc_tcost;

    // Fast lookup for cell port to net user index
    dict<std::pair<IdString, IdString>, size_t> fast_port_to_user;

    // Fast lookup for cell to clusters
    dict<ClusterId, std::vector<CellInfo *>> cluster2cell;

    // Wirelength and timing cost at last and current iteration
    wirelen_t last_wirelen_cost, curr_wirelen_cost;
    double last_timing_cost, curr_timing_cost;

    Context *ctx;
    float temp = 10;
    float crit_exp = 8;
    float lambda = 0.5;
    bool improved = false;
    int n_move, n_accept;
    int diameter = 35, max_x = 1, max_y = 1;
    dict<IdString, std::tuple<int, int>> bel_types;
    dict<IdString, BoundingBox> region_bounds;
    FastBels fast_bels;
    pool<BelId> locked_bels;
    std::vector<NetInfo *> net_by_udata;
    std::vector<decltype(NetInfo::udata)> old_udata;
    bool require_legal = true;
    const int legalise_dia = 4;
    Placer1Cfg cfg;

    TimingAnalyser tmg;
};

Placer1Cfg::Placer1Cfg(Context *ctx)
{
    constraintWeight = ctx->setting<float>("placer1/constraintWeight", 10);
    netShareWeight = ctx->setting<float>("placer1/netShareWeight", 0);
    minBelsForGridPick = ctx->setting<int>("placer1/minBelsForGridPick", 64);
    budgetBased = ctx->setting<bool>("placer1/budgetBased", false);
    startTemp = ctx->setting<float>("placer1/startTemp", 1);
    timingFanoutThresh = std::numeric_limits<int>::max();
    timing_driven = ctx->setting<bool>("timing_driven");
    slack_redist_iter = ctx->setting<int>("slack_redist_iter");
    hpwl_scale_x = 1;
    hpwl_scale_y = 1;
}

bool placer1(Context *ctx, Placer1Cfg cfg)
{
    try {
        SAPlacer placer(ctx, cfg);
        placer.place();
        log_info("Checksum: 0x%08x\n", ctx->checksum());
#ifndef NDEBUG
        ctx->lock();
        ctx->check();
        ctx->unlock();
#endif
        return true;
    } catch (log_execution_error_exception) {
#ifndef NDEBUG
        ctx->lock();
        ctx->check();
        ctx->unlock();
#endif
        return false;
    }
}

bool placer1_refine(Context *ctx, Placer1Cfg cfg)
{
    try {
        SAPlacer placer(ctx, cfg);
        placer.place(true);
        log_info("Checksum: 0x%08x\n", ctx->checksum());
#ifndef NDEBUG
        ctx->lock();
        ctx->check();
        ctx->unlock();
#endif
        return true;
    } catch (log_execution_error_exception) {
#ifndef NDEBUG
        ctx->lock();
        ctx->check();
        ctx->unlock();
#endif
        return false;
    }
}

NEXTPNR_NAMESPACE_END